Recovery of solvents



March 1931. J. F. WAIT 1,798,713

RECOVERY OF SOLVENTS Filed Dec. 31; 1924 N M ONIH A D A M LING; WATER /0 Coouruq WATER If f flMmoN m as PARA-r0 2 m TO ABSORBER LCOHOL- T0 .sroRnqE ALCOHOL REFLUX CooLnuq WATER w, INVENTOR MMTTORNEY Patented Mar. 31, 1931 r orric JUSTIN F. WAIT, OF NEW YORK, N. Y., ASSIGNOR IO NATIONAL ANILINE & CHEMICAL 00., INC., A CORPORATION OF NEW YORK RECOVERY OF SOLVEN'IS Application filed December 31, 1924. Serial No. 759,048.

It has been found that in carrying out many chemical processes that it is desirable first to dissolve in a solvent the substance that is to undergo chemical reaction. In many instances of reactions of this character, gases are sometimes formed which become dissolved in the solvent and the solvent also becomes diluted to such a great extent that it needs to be concentrated and the gas removed therefrom before being reused.

By the present invention solvents can be recovered after they have been used for solvent processes and they can at the same time be concentrated, and also substantially all of the gases that have become dissolved therein can be eliminated in' a very effective and rapid manner. In carrying out this invention the crude dilute solvent is treated in such a manner that it is caused to pass in a vapor stage through or in contact with a series of batches of liquid so arranged that as the solvent vapors pass from one batch of liquid to another, the desired condensation is caused to take place after which the gas that may be dissolved in the solvent may be liberated and the solvent vapors may be condensed and segregated. Another feature of this invention is that after the gases have been eliminated from the solvent they may be cooled so as to recover solvent that may be present therewith and to better adapt the gases for immediate use. The condensed solvent may also be cooled to reduce losses by evaporation. The initial or preliminary part of the process will, in most cases, require that the entire solvent vapors be condensed and returned as back-flow in a dephlegmator while the major portion of the gases is being removed, after which the condensate from the solvent vapors may be divided in such a manner that the requisite amount is used as back-flow for the dephlegmator column while the remaining portion is carried away to a receiver or for reuse.

In carrying .out the process it has been found that whenever desirable it is possible to obtain a very concentrated solution of the gas in the solvent while segregating this gas solvent solution from the remaining materials. By this process the solvent can be concentrated to suflicient extent to adapt it for immediate reuse.

In the accompanying drawings, an apparatus is illustrated by which the process can be carried out. It is obvious that many different arrangements of apparatus may be utilized for carrying out the process without departing from the spirit or scope of the invention.

The drawing is a sectional view in elevation in which reference character 1 indicates a column, the lower portion of which may be heated in any convenient manner. As shown in the drawings, the heat may be applied by means of a steam chest 2 which has tubes 3 extending through the lower end of the column 1. The column 1 is arranged with the usual plates 4 which are provided with overflow pipes 5 as well as the caps 6 and nozzles 7 A pipe 8 extends from the top of the column through the cooler 16 for carrying away and cooling the uncondensed gases that may be separated.

A. specific example of a process embodying this invention is the production of the sodium salt of phenylglycine by the interaction of aniline, formaldehyde and sodium cyanide in an alcoholic solution. Ammonia gas is liberated during the reaction and, at the end of the reaction cycle, there is obtained a mixture of an alcoholic solution of ammonia, water, aniline and the sodium salt of phenylglycine.

The requirements for commercial operation of this process include recovery of both the alcohol and the ammonia, and, as the reaction is best carried outwith an excess of aniline, it includes recovery of the excess aniline. It has been found that if the alcohol. is to be reused in subsequent reaction cycles it must be substantially free from ammonia and its concentration must be increased in order to give satisfactory yields, It is desirable, therefore,

to both isolate and recover the ammonia and to concentrate and recover the alcohol.

The recovery of ammonia is best effected by distilling the mass resulting from the reaction, through the equipment described or its equivalent, and by returning the condensate from condenser 9 through the separator 11 to the column 1 while removing ammonia gases through the pipe line 15. After this removal of gases has continued for an appreciable time, the ammonia content of the mass gradually decreases and the condensed liquid, which is mainly alcohol, contains but small amounts of ammonia. When the amount of ammonia in the condensate has decreased to about 1%, a portion of the condensate is collected from the pipe 13 and isolated, this operation continuing as long as the concentration of alcohol is above'9O%, which is preferred for subsequent reaction cycles. This usually gives a recovered alcohol of a strength of about 91% and with an ammonia content of les n 1 6% By proper use of a fractionating column, it is generally possible to recover practically all of the alcohol at a satisfactory concentra tion and of allowable ammonia content. The operator can, by trial, control the ratio of the back-flow through pipe 12 to forward flow through pipe 13, by means of the valves 20 and 21,, so as to procure the desired concentration of alcohol. Small portions of alcoholcont-aining liquid are drawn off through line 13 into special receivers for recovery in a subsequent fractionating cycle.

For the recoverv of the. aniline the fractionating column may be eliminated and the aniline removed from the mixture by steam distillation involving .either the direct injection of steam or generation thereof by means of the heating tubes 3. A somewhat more preferable method for recovering the aniline includes indirect heating to distill the water and aniline vapors, condensation of the vapors, and continuous separation of the water layer from the aniline layer, the former returning to the still for re-evaporation and the latter being isolated and recovered. Either of these methods will remove aniline from the liquid mass containing the phenylglycine salt. When a sufficient quantity of aniline has been removed the mass is dried producing a dry salt useful for the manufacture of indigo or other products, I

During the preliminary refluxing stage wherein the ammonia is removed from the separator 11 through pipe 15 and wherein the condensate is all or substantially all returned through the pipe line 12, the ammonia content of the system is gradually reduced and .the successive portions of the condensate contain smaller amounts of ammonia. If the alcohol is to be reused in the phenylglycine process, it is preferably isolated after the ammonia content thereof has been reduced below 3% so that the average ammonia content of the alcohol recovered is below In special instances where an alcohol solution of ammonia can be used in another process, as forexample, in the manufacture of diphenylguanidine, it is desirable to isolate the concentrated ammonia and use it practically as it is recovered. Alcohol with an ammonia content above and containing less than water is usually satisfactory for such types of reaction. If such an alcohol is desired to be recovered, portions of the reflux mass may be isolated before the ammonia content there of has been reduced to 3%.

In operating-the process on a commercial scale the temperature of the cooling water in the condenser 9 is frequently high and the ammonia gas passing through the line 15 sometimes contains appreciable quantities of alcohol vapor. To reduce these losses and likewise to cool the ammonia gas so that it may be more readily utilized, a condenser containing ice water or cooled by direct expansion of ammonia or by a brine circulating system is used as shown at 16. Likewise the condensed vapors are frequently at so high a temperature that there will be appreciable evaporation losses when these vapors come into contact with the atmosphere. A special condenser shown at 14 is, therefore, sometimes provided to cool the condensate and prevent these losses.

I claim:

l. The process which comprises causing aniline, an alkali-metal cyanide and formaldehyde to react in a solvent comprising alcohol and water to produce a reaction mixture containing an akali-metal phenyl glycinate, alcohol, aniline, ammonia and water, vaporizing liquids from the reaction mixture, condensing the vapors, separating ammonia from the condensate, refluxing substantially all of said condensate and bringing it into contact with said vapors, and continuing said operations of distillation, condensation, separation of ammonia, and returning of condensate until the condensate contains only a small amount of ammonia, and then withdrawing a portion of the condensate from the system while continuing said distillation and condensation.

2. The process which comprises causing aniline, a cyanide and formaldehyde to react in the presence of alcohol and water, vaporizing liquids from the reaction mixture, condensing the vapors, separating ammonia gas from the condensate, refluxing condensate in contact with the vapors, subsequently'separating and recovering a portion of the condensate containing a small amount of ammonia, and subsequently forming therewith a reaction mixture containing aniline, a cyanide and formaldehyde.

3. The process which comprises causing aniline, a cyanide and formaldehyde to react in the presence of alcohol and water, distilling olf liquids contained in the reaction mixture, condensing the vapors, separating ammonia gas from the condensate, returning condensate for redistillation, subsequently diverting portions of condensate for recovery of alcohol, distilling oif aniline and water, separating aniline from the distillate, and returning aniline containing water for redistillation.

4. The process which comprises causing aniline, a cyanide and formaldehyde to re act in the presence of alcohol and Water, distilling off liquids contained in the reaction mixture, condensing the vapors, separating ammonia gas from the condensate, returning condensate for redistillation, subsequently diverting portions of condensate containing less than 3% of ammonia and less than 15% of water for recovery of alcohol, distilling olf aniline and water, separating aniline from the distillate, and returning aniline containing water for redistillation.

5. The process which comprises causing aniline, a cyanide and formaldehyde to re act in the presence of alcohol and water, vaporizing liquids from the reaction mixture, condensing the vapors, separating ammonia gas from the condensate, refluxing the condensate in contact with the vapors, subsequently separating and recovering a portion of the condensate containing less than 1 percent of ammonia, and subsequently forming therewith a reaction mixture containing aniline, a cyanide and formaldehyde.

6. The process which comprises causing aniline, a cyanide and formaldehyde to react in the presence of alcohol and water,

vaporizing liquids from the reaction mixture,

condensing the vapors, separating ammonia gas from the condensate, returning condensate for redistillation, and continuing said operations of distillation, condensation, separation of ammonia and returning of condensate until said condensate contains less than 3 per cent of ammonia, then withdrawing a portion of the condensate from the system while continuing said distillation and condensation, and subsequently mixing aniline, a cyanide and formaldehyde therewith to form a reaction mixture.

7. The process which comprises causing aniline, an alkali-metal cyanide and formaldehyde to react in the presence of alcohol and water to produce a reaction mixture containing an alkali-metal phenylglycinate, alcohol, aniline, ammonia and water, vaporizing liquids from the reaction mixture, condensing the vapors, separating ammonia gas from the condensate, returning substantially all of the condensate and bringing it into contact with said vapors, continuing said operations of distillation, condensation, separation of ammonia and return of condensate until said condensate contains less than 3 per cent. of ammonia, then withdrawing from the system a portion of the condensate containing alcohol and less than 15 per cent. of water while continuing said distillation and condensation, and subsequently mixing aniline, alkali metal cyanide and formaldehyde with said withdrawn condensate to form a reaction mixture.

8. The process which comprises causing aniline, an alkali-metal cyanide and formaldehyde to react in the presence of alcohol and water, vaporizing liquids from the reaction mixture, condensing the vapors, separating, 

